The spectral distribution of light generated by a finite cavity with one moving mirror is compared with that produced by a fixed cavity containing a time-varying dielectric. In both cases a motion over a finite time interval is considered. Although the moving mirror is usually considered to be an idealization for the time-varying dielectric, there are qualitative differences in the spectra produced. The spectral distribution for the moving mirror case behaves as 1/${\mathit{n}}^3$, while that for the time-varying dielectric behaves on average as 1/${\mathit{n}}^4$ but is rapidly oscillating.

• Received 1 July 1994

DOI:https://doi.org/10.1103/PhysRevA.51.4109